Alan 91 C2

Looking at the internal power brake horse power (BHP) required to get around 300 RWHP. If we start with say, 35 pounds of fuel per hour, per injector, then cranking through the Stoichiometry, we are moving 6 pounds of fuel per minute, for say 66 pounds of air to fuel at 11:1.

An N/A motor might operate at 28% efficiency, whereas the turbo motor creates more shaft power. The turbo yields the end result of more displacement=more HP.

Anyone have data on the Turbocharger BHP?

What is the turbine inlet pressure at say 6,000 RPM and 15 PSI outlet PSI, for 951 as original plumbing?

The flows through the tiny 951 air intake system, yield massive pressure drop (PD). Anyone tested the PD?

V2Rocket

a centrifugal supercharger can take 30-40hp to drive at the boost levels/power levels 951 guys usually hang around in.

but they have some extra losses from belt and gear friction in there, so maybe 25-30?

how would you imagine to measure such a thing on say an engine dyno?

TurboTommy

What are you asking, exactly?
How much crank power is lost in order to drive the turbo?

I did this excercise once and came up with about 15 crank bhp on a stock turbo S , roughly; But I forget now how I came up with that.
Basically, the crank power losses are incurred because of the negative difference between the turbine inlet pressure and the boost pressure generated. But, then you can add some net power back in because of the higher mechanical efficiency achieved.
Obviously, trying to squeeze more power from a smaller turbo (especially the hotside) will cost relatively a higher percenatge of crankshaft power.
I read a tech article once that stated that the turbos on a 993tt have a shaft power of 32 hp combined; but, I'm not sure if you can correlate that to how much crank power would be needed to drive them. And then, again, you can add net power back in because of power achieved from the boost pressure generated. So, I think we're close.

I wouldn't say there are "massive pressure drops" through the stock intake system.
Maybe about 1.5 psi through the AFM and 1.5 psi through the IC on a stock car.

Alan 91 C2

Some of the online calculators show over 35 BHP for the Turbocharger compression at 15 PSI. But when you look at the efficiency of both the cold and hot side fans, input total hp could approach 100hp.

at (35 #gas /hr * 4 cyl/6.4 pound/gal)= 21.8 gal/hr

Total combustion heat = 21.8 gal * 100,000 BTU/gal= 2.18 mil BTU/Hr.

allow 30% for mechanical conversion, so waste at 1.4 Mil BtuH.

Allow avg heat dissipation at say 500,000 BtuH then temp rise is about 100 deg F, assuming 5000 CFM of radiator air flow.

Alan 91 C2

Thanks Tommy,

I am thinking maybe several PSI total loss to the inlet of the turbo at upper RPM.

And yes the power to run the turbo is an internal load to the engine, but not a shaft load on the engine. But there is an equivalent BHP on the exhaust gas side, calculated by the airflow and pressure on the cold side of the turbo, with allowance for efficiency, best around 70%.

I will set up my pressure logger and measure the DP in a few weeks.

TurboTommy

The ambient airflow on a stock turbo S , at full power, is 350 CFM.

There is a crankshaft load because of the turbo, which is the pumping loss, which is the difference in pressure the pistons see to pump air in and out of the engine. This is the only load that matters here, because it's the power you don't have available to drive the rear wheels. But, it's not much in a well designed system.

Alan 91 C2

I was searching and found the below.
https://rennlist.com/forums/944-turb...6-k27-2-a.html

The graph shows the upper flow at ~0.1-0.2 cu Meter/second. The flow would be

=3.28*3.28*3.28(ft/M3) *60*.17 M3/s
=360 CFM

Took a calculation ride.